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kirza4 [7]
3 years ago
15

A national survey of middle-school students asks which subject is most challenging. Which of these samples is a representative s

ample? A. 372 sixth-graders in a certain town B. 972 seventh-graders in a certain county C. 619 eighth-graders in different states D. 400 students from various states, representing different grades, 6–8
Mathematics
1 answer:
Bezzdna [24]3 years ago
7 0
The answer would be D, since a representative sample is a set chosen from a larger statistical population.
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A large tank is filled to capacity with 300 gallons of pure water. brine containing 5 pounds of salt per gallon is pumped into t
Licemer1 [7]
If A(t) is the amount of salt in the tank at time t, then the rate at which this amount changes over time is given by the ODE

A'(t)=\dfrac{3\text{ gal}}{1\text{ min}}\cdot\dfrac{5\text{ lb}}{1\text{ gal}}-\dfrac{3\text{ gal}}{1\text{ min}}\cdot\dfrac{A(t)\text{ lb}}{300+(3-3)t\text{ gal}}

A'(t)+\dfrac1{100}A(t)=15

We're told that the tank initially starts with no salt in the water, so A(0)=0.

Multiply both sides by an integrating factor, e^{t/100}:

e^{t/100}A'(t)+\dfrac1{100}e^{t/100}A(t)=15e^{t/100}
\left(e^{t/100}A(t)\right)'=15e^{t/100}
e^{t/100}A(t)=1500e^{t/100}+C
A(t)=1500+Ce^{-t/100}

Since A(0)=0, we have

0=1500+C\implies C=-1500

so that the amount of salt in the tank over time is given by

A(t)=1500(1-e^{-t/100})

After 10 minutes, the amount of salt in the tank is

A(10)=1500(1-e^{-1/10})\approx142.74\text{ lb}
8 0
3 years ago
NEED HELP ASAP WILL MARK BRAINLIEST!!
Anettt [7]

Answer:

Step-by-step explanation:

Hi there!

Here;

The question is: 3÷ \frac{1}{6}

→ Take reciprocal of 1/6, then;

   = 3*\frac{6}{1}

   = 18

So, the answer is option D.

Hope it helps!

8 0
2 years ago
Read 2 more answers
Here are eight angles. Which of these angles are acute angles?
Alexeev081 [22]

Answer:a and b

Step-by-step explanation:an acute angle in small, an acute angle will always be smaller then C

5 0
2 years ago
Shawn has $20.00 to spend. He wants to save $5.00. He buys two ice creams for $1.65 each, what is the maximum number of packets
LenKa [72]

Answer:

3

Step-by-step explanation:

3.45x+2*1.65+5>=20

3.45x+8.3>=20

3.45x>=11.7

after rounding

x>=3

4 0
2 years ago
Please answer !!!!!!!!!!!! Will mark Brianliest !!!!!!!!!!!!!!!!
lbvjy [14]

Answer:

x = 55 degrees

Step-by-step explanation:

180 - 164 = 16. 16 + 109 = 125. A triangle's angles should add up to 180, so to find the value of x, subtract 180 by 125 and you'll get 55.

7 0
3 years ago
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